The objective of the proposed project is to understand the range of plasticity in non-human primate vocal behavior and the factors that influence variation. The specific aims will be 1) to assess several possible mechanisms underlying plasticity in the vocal behavior of a non-human primate species, and 2) to experimentally test the underlying mechanisms in non-human primate vocal plasticity. Following research on songbirds and anurans, I will make acoustic recordings and behavioral observations of vocal behavior in several geographically separated populations of a single non-human primate species. By documenting geographic variation in vocal communication, it will be possible to ascertain the role of several possible mechanisms that underlie plasticity in non-human primate vocal behavior. A series of plasticity is a product of specific mechanisms. Specifically, the first series of playback experiments will be used to determine whether non-human primates adapt the acoustic structures of their vocalizations to maximize transmission through the environment. The second set of playback experiments will investigate the plasticity in the alarm call system for adapting to sympatric predators.